Method for transitioning radio resource control state of user equipment to idle state, system therefor, and the same user equipment

ABSTRACT

In a WCDMA mobile communication system, when the amount of packet traffic transmitted to or received from a UE decreases during a predetermined time in a CELL_DCH state in which a WCDMA packet data connection has been established, the UE transitions to a CELL_FACH state by a radio network controller (RNC). Thereafter, it is determined if there is no transmitted or received packet traffic during a certain time in the CELL_FACH state (which is an RRC state in which an RRC connection has been connected, and the dedicated physical channel has been released). When it is determined that there is no transmitted or received packet traffic during the certain time, the UE requests a network to release the RRC connection by utilizing a Signaling Connection Release Indication (SCRI) message. The invention enables a UE to check a packet transmission or reception flow, and to directly transmit the SCRI message to the network.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is a continuation of U.S. patent applicationSer. No. 12/082,398 filed Apr. 10, 2008, which is related to and claimsthe benefit under 35 U.S.C. §119(a) of an application entitled “METHODFOR TRANSITIONING RADIO RESOURCE CONTROL STATE OF USER EQUIPMENT TO IDLESTATE, SYSTEM THEREFOR, AND THE SAME USER EQUIPMENT” filed in the KoreanIndustrial Property Office on Apr. 13, 2007 and assigned Korean PatentApplication Serial No. 10-2007-0036670. The present application claimspriority to both U.S. patent application Ser. No. 12/082,398 and KoreanPatent Application Serial No. 10-2007-0036670, the contents of both ofthese applications are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a WCDMA mobile communication system,and more particularly to a method for transitioning the radio resourcecontrol state of a user equipment (UE) to an idle state, a systemtherefor, and the same UE.

BACKGROUND OF THE INVENTION

A WCDMA mobile communication system provides a MultimediaBroadcast/Multicast Service (MBMS) to user equipments (UEs). The MBMS isa service for transmitting data packets to users.

FIG. 1 is a block diagram illustrating the configuration of a WCDMAmobile communication system supporting such an MBMS.

The WCDMA mobile communication system includes at least one UE 10 and/or12 for receiving the MBMS, a UMTS Terrestrial Radio Access Network(UTRAN) containing a node B 20 and a radio network controller (RNC) 30,a Serving GPRS Support Node (SGSN) 40 belonging to a core network (CN),a Home Location Register (HLR) 42, a Gateway GPRS Support Node (GGSN)(not shown), and a packet network 50 for transmitting packet data.

The UE 10 or 12 is connected to the node B 20 and the UTRAN so as toprocess a call, supports both circuit service (CS) and packet service(PS), and includes hardware and software for receiving MBMS data. Thenode B 20 is connected to the UE 10 or 12 via a Uu interface, and theRNC 30 is connected to the SGSN 40 via an Iu interface.

The UTRAN performs a protocol conversion process to transfer radiofrequency (RF) data control messages, transmitted from the UE 10 or 12over the air, to the CN using a GPRS Tunneling Protocol (GTP). In thiscase, the GPRS (General Packet Radio Service) is a packet data serviceprovided in the UMTS network. The SGSN 40 is a network node for managingsubscriber and position information of the UE 10 or 12. The SGSN 40 isconnected to the UTRAN via an Iu interface, and transmits/receives data,control messages, etc. to/from the packet network 50. The SGSN 40 isconnected to the HLR 42 via a Gr interface, and manages the subscriberinformation and position information. The HLR 42 stores subscriberinformation of a packet domain, routing information, etc. The HLR 42 isconnected to the SGSN 40 via a Gr interface. A message flow fortransmitting/receiving packet data in a WCDMA mobile communicationsystem having the aforementioned construction will now be described withreference to FIG. 2.

First, in order for the UE 10 and the RNC 30 to transmit or receivepacket data therebetween, a radio resource control (RRC) connection mustbe set between the UE 10 and the RNC 30.

The RRC connection set between the UE 10 and the RNC 30 may have one ofthree states (i.e., a CELL_DCH state, a CELL_FACH state, and an IDLEstate) and transitions between the CELL_DCH state, the CELL_FACH stateand the IDLE state according to the volume of packet data traffictransmitted and received between the UE 10 and the RNC 30.

The CELL_DCH state refers to a 3GPP WCDMA RRC state, and represents astate in which the RRC connection and a dedicated physical channel areconnected between a UE and a node B (i.e. UTRAN) in a WCDMA network. Inthe CELL_DCH state, a large amount of packet data is actuallytransmitted or received.

The CELL_FACH state refers to a 3GPP WCDMA RRC state, and represents astate in which the dedicated physical channel is released and the RRCconnection is maintained. In the CELL_FACH state, an S-CCPCH (FACH) iscontinuously monitored, and a small amount of uplink or downlink packetdata can be transmitted or received.

The IDLE state represents a state in which both RRC connection anddedicated physical channel have been released. In the IDLE state, only apaging indication channel (PICH) is monitored, and it is possible toenter a WCDMA protocol sleep state.

Referring to FIG. 2, the UE 10 transmits an RRC connection setup requestmessage to the RNC 30 in step 102. When receiving the RRC ConnectionSetup Request message, the RNC 30 transmits an RRC Connection Setupmessage to the UE 10 in step 104. When receiving the RRC ConnectionSetup message, the UE 10 transmits an RRC Connection Setup Completemessage to the RNC 30 in response to the RRC Connection Setup message,thereby setting an RRC connection between the UE 10 and RNC 30.

Then, the UE 10 performs a packet data protocol (PDP) Context Activationprocedure for packet data communication. In detail, the UE 10 transmitsa PDP Context Activation Request message to the SGSN 40 in step 108.When receiving the PDP Context Activation Request message from the UE10, the SGSN 40 transmits a PDP Context Activation Accept message to theUE 10 in step 110, thereby enabling the UE 10 to perform packetcommunication.

After the PDP Context Activation procedure, uplink and downlink packetdata traffic is transmitted between the UE 10 and the SGSN 40 in step112. Thereafter, when there is no packet data traffic transmittedbetween the UE 10 and the SGSN 40 in step 114, the RNC 30 changes astate of a physical channel established between the UE 10 and RNC 30 instep 116. In other words, when the volume of packet data traffictransmitted to or received from the UE 10 is reduced, the RNC 30transitions to the CELL_FACH state. Subsequently, when the RNC 30determines that there is no more packet data traffic transmitted in step118, the RNC 30 proceeds to step 120, where the RNC 30 transmits an RRCConnection Release message to the UE 10. In response to the RRCConnection Release message, the UE 10 transmits an RRC ConnectionRelease Complete message to the RNC 30 in step 122, so that the RRCconnection transitions to the IDLE state.

As described above, according to the conventional WCDMA 3GPP standard,while packet data is being transmitted/received after signaling fortransmission of packet data has been achieved between the UE 10 and theSGSN 40, if the volume of packet data traffic is reduced, the RNC 30releases the RRC connection, and instructs the UE 10 to transition theRRC state from the CELL_FACH (or CELL_DCH) state to the IDLE state.

Through this, the UE 10 releases the RRC connection, and transitionsfrom the CELL_FACH (or CELL_DCH) state to the IDLE state, therebyentering a sleep state in terms of protocol. When the UE 10 has enteredthe sleep state, power consumption is minimized, so that it is possibleto stably manage the battery thereof.

However, some WCDMA networks have a problem in that they do not releasethe RRC connection or that they release the RRC connection too late,although there is no more packet data traffic being transmitted in theCELL_FACH state.

According to the conventional technology, there is no way for the UE 10to transition from the CELL_FACH state to the IDLE state, except forfollowing the control of the network. Therefore, the UE 10 mustcontinuously monitor a dedicated control channel (DCCH), a radio accesschannel (RACH) and a forward access channel (FACH) while in the CELL_DCHstate, and must continuously monitor the FACH and the RACH while in theCELL_FACH state, so that unnecessary current consumption is caused,thereby decreasing the battery lifetime.

Also, among smart phones recently highlighted in the 3G market,WinCE-based phones have a menu which is configured in such a manner asto release a cellular connection by a wireless manager, so that theWinCE-based phone does not release the PDP connection, even when the Endkey is pressed, unlike other general phones, thereby having a highprobability of causing the aforementioned problem.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object to provide a method for transitioning the state of a userequipment (UE) to an idle state, a system therefor, and the same UE.

In accordance with an aspect of the present invention, there is provideda system for transitioning a radio resource control (RRC) state of auser equipment to an idle state, the system including: the userequipment for transmitting a Signaling Connection Release indication(SCRI) message when packet data traffic transmitted to/received from theuser equipment has not been generated during a predetermined time; and aradio network controller (RNC) for transmitting an RRC ConnectionRelease message to the user equipment when the RNC has received the SCRImessage from the user equipment.

In accordance with another aspect of the present invention, there isprovided a method for transitioning a radio resource control (RRC) stateof a user equipment to an idle state by the user equipment, the methodincluding the steps of: determining if packet data traffic transmittedfrom/received to the user equipment has not been generated during apredetermined time; and transmitting a Signaling Connection ReleaseIndication (SCRI) message to a radio network controller (RNC) when thepacket data traffic transmitted from/received to the user equipment hasnot been generated during a predetermined time.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 is a block diagram illustrating the configuration of aconventional WCDMA mobile communication system;

FIG. 2 is a flow diagram illustrating a message flow for packet datatransmission/reception in the conventional WCDMA mobile communicationsystem;

FIG. 3 is a flow diagram illustrating a method for transitioning to theIDLE state in a WCDMA mobile communication system according to anexemplary embodiment of the present invention;

FIG. 4 is a block diagram illustrating the configuration of a userequipment (UE) according to an exemplary embodiment of the presentinvention;

FIG. 5 is a flowchart illustrating a method for transitioning to theIDLE state by the UE according to an exemplary embodiment of the presentinvention;

FIG. 6 is a flowchart illustrating a method for measuring the volume ofpacket data traffic according to an exemplary embodiment of the presentinvention; and

FIG. 7 is a flow diagram illustrating a mechanism for internallygenerating an SCRI transmission instruction by the UE according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 3 through 7, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication system.

According to the present invention, there is provided a method forsolving an inefficient current consumption problem which is causedbecause a WCDMA network attempts to transition a radio resource control(RRC) state to an IDLE state when there is no packet data actually beingtransmitted/received in a packet data transmission/reception stage, asystem for the method, and an operation method of a user equipment (UE)therefor.

According to an exemplary embodiment of the present invention, in aWCDMA mobile communication system, when the amount of packet traffictransmitted to or received from a UE decreases during a predeterminedtime in a CELL_DCH state (which is an RRC state in which a dedicatedphysical channel has been connected), in which a WCDMA packet dataconnection has been established, the UE transitions to a CELL_FACH stateby a radio network controller (RNC). Thereafter, it is determined ifthere is no transmitted or received packet traffic during a certain timein the CELL_FACH state (which is an RRC state in which an RRC connectionhas been connected, and the dedicated physical channel has beenreleased). When it is determined that there is no transmitted/receivedpacket traffic during the certain time, the UE requests a network torelease the RRC connection by utilizing a Signaling Connection ReleaseIndication (SCRI) message.

According to the conventional WCDMA 3GPP standard (3GPP TS 25.331), itis stipulated that the SCRI message should be transmitted by a UE eitherwhen the UE fails in an RRC connection in a network, or when a time-outof transmission/reception of a dedicated control channel (DCCH) messageon an RRC connection occurs. In contrast, according to the presentinvention, a UE checks a packet transmission/reception flow, and candirectly transmit the SCRI message to the network.

In addition, according to an exemplary embodiment of the presentinvention, when an Iu Release request is transmitted between a radionetwork controller (RNC) and an SGSN under the above situation, the RNCestablishes “cause 40” in the Iu Release request, and transmits the IuRelease request to the SGSN. When the SGSN receives the Iu Releaserequest with the “cause 40,” the SGSN can terminate only the Iusignaling connection while maintaining the PDP connection.

FIG. 3 is a flow diagram illustrating a method for transitioning to theIDLE state in a WCDMA mobile communication system according to anexemplary embodiment of the present invention.

In step 501, a UE 200 determines if an SCRI transmission condition issatisfied. The SCRI transmission condition is a condition fortransmitting an SCRI message from the UE 200 to an RNC 300. In detail,the UE 200 periodically reports the volume of packet data traffictransmitted from/received to the UE 200 to the RNC 300. Then, the RNC300 instructs the UE 200 to transition to the CELL_FACH state based onthe reported volume of packet data traffic. The UE 200 transitions tothe CELL_FACH state, and then determines if the SCRI transmissioncondition is satisfied.

According to an exemplary embodiment of the present invention, whenthere is no packet data traffic transmitted from/received to the UEduring a certain time or certain period, it is determined that the SCRItransmission condition is satisfied. In this case, the UE 200transitions to the CELL_FACH state, and then determines if packet datatraffic transmitted from/received to the UE 200 has not been generatedduring a certain time. According to another exemplary embodiment of thepresent invention, the UE 200 may determine if packet data traffictransmitted from/received to the UE 200 has not been generated during acertain time in the CELL_DCH state. It will be understood by thoseskilled in the art that various SCRI transmission conditions may beestablished depending on operators or systems.

When the SCRI transmission condition has been satisfied, the UE 200transmits an SCRI message to the RNC 300 in step 503. In this case, ifonly a packet switching domain service is currently in activation, theUE 200 only has to record “ps” as a factor of the SCRI and to transmitan SCRI message, and if the UE 200 is in a multi-RAB (Radio AccessBearer) situation (e.g. CS+PS: a case where a Circuit Switching DomainDedicated Resource and a Packet Switching Domain Dedicated Resource aresimultaneously allocated to and used by the UE 200), the UE 200transmits an SCRI message to the RNC 300 after the CS domain service(e.g. voice call) has been completed.

When receiving the SCRI message, the RNC 300 transmits an Iu ReleaseRequest message to an SGSN 400 in step 505. In this case, a cause valueincluded in the Iu Release Request message is set to “cause 40 (Releasedue to UE generated signaling connection release).”

Since the cause value included in the received Iu Release Requestmessage has been set to “cause 40,” the SGSN 400 can determine that theRNC 300 requests the SGSN 400 to release an Iu signaling connection, butto maintain a PDP connection. Accordingly, the SGSN 400 transmits an IuRelease Command message to the RNC 300 in step 507 in order to preservethe PDP connection and to release the Iu signaling connection.

When receiving the Iu Release Command message, the RNC 300 releases anIu signaling connection resource, and transmits an Iu Release Completemessage to the SGSN 400 in step 509. Thereafter, the RNC 300 transmitsan RRC Connection Release message to the UE 200 in step 511 in order torelease an RRC connection with the UE 200.

After receiving the RRC Connection Release message, the UE 200 changesthe RRC state to the IDLE state while transmitting an RRC ConnectionRelease Complete message to the RNC 300 in step 513, which can achieve astate transition to a sleep state in terms of protocol, thereby largelyreducing the amount of current consumption.

FIG. 4 is a block diagram illustrating the configuration of the UEaccording to an exemplary embodiment of the present invention.Preferably, the UE 200 may be a smart phone according to an exemplaryembodiment of the present invention.

The UE 200 includes a PDA unit 210, a display unit 220, and a modem unit230. The modem unit 230 includes a protocol task section 232. Theprotocol task section 232 communicates with a WCDMA network, transferspacket data from the network to the PDA unit 210, and transmits variousdata from the PDA unit 210 to the network. In addition, the protocoltask section 232 monitors the volume of packet data traffictransmitted/received between the UE 200 and the network.

The PDA unit 210 includes an operating system (OS) 212, a radiointerface layer (RIL) 214, and an interface task section 216. Theinterface task section 216 performs interfacing with the modem unit 230.The interface task section 216 monitors the volume of packet datatraffic transmitted/received between the interface task section 216 andthe modem unit 230. In addition, the interface task section 216receives, from the protocol task section 232, information about thevolume of packet data traffic transmitted/received between the UE 200and the network. The interface task section 216 determines if the SCRItransmission condition is satisfied, based on the volume of packet datatraffic transmitted/received between the interface task section 216 andthe modem unit 230, and the volume of packet data traffictransmitted/received between the UE 200 and the network.

As described above, the SCRI transmission condition is satisfied whenpacket data traffic transmitted from/received to the UE has not beengenerated during a certain time. To this end, the interface task section216 may include a certain timer (not shown), or may use an existingtimer within the PDA unit 210.

When the SCRI transmission condition is satisfied, the interface tasksection 216 notifies the RIL 214 that it is necessary to enter a PDPPreservation state. The PDP Preservation state represents a state inwhich a PDP connection is preserved while an Iu signaling connection hasbeen released.

The RIL 214 interfaces, for example, an operating system for a wirelessUE, such as a CellCore layer of a Windows Mobile, with a wirelessprotocol stack within the modem chip 230. In addition, when the RIL 214receives the report that it is necessary to enter the PDP Preservationstate from the interface task section 216, the RIL 214 transfers thenotification for the PDP Preservation to the operating system 212.

Upon receiving the notification for the PDP Preservation from the RIL214, the operating system 212 calls an RIL application programminginterface (RIL API). Then, the RIL 214 instructs the interface tasksection 216 to transmit an SCRI message to the network according to thecalled RIL API. The interface task section 216 instructs the RRC totransmit an SCRI to the RNC 300, in response to the instruction of theRIL 214.

A control flow for transitioning to the IDLE state by the UE will now bedescribed with reference to FIG. 5.

FIG. 5 is a flowchart illustrating a method for transitioning to theIDLE state by the UE according to an exemplary embodiment of the presentinvention.

First, the UE 200 periodically measures and reports the volume of packetdata traffic to the RNC 300. The network, i.e. the RNC 300, changes theRRC state of the UE 200 based on the volume of packet data trafficreported from the UE 200. The following description will be given on theassumption that the UE 200 periodically measures the volume of packetdata traffic.

Referring to FIG. 5, in step 600, the UE 200 is in the CELL_FACH state.As described above, the CELL_FACH state represents a state in which adedicated physical channel has been released while the RRC connection ismaintained. In the CELL_FACH state, the UE 200 can transmit or receive asmall amount of uplink or downlink packet data to or from the network.

When the UE 200 has entered the CELL_FACH state, the UE 200 determinesif there is packet data traffic transmitted to/received from the RNC 300in step 610. If it is determined that there is no transmitted/receivedpacket data traffic, the UE 200 proceeds to step 620, where the UE 200drives a timer “T_notraffic.” The operating time of the timer isappropriately determined so as to prevent the UE 200 from beingmaintained in the CELL_FACH state and consuming battery power during notransmitted/received packet data traffic.

In detail, the operating time of the timer, i.e. a timer value, isdetermined to be an appropriate value for at least driving the timerdirectly after packet traffic is measured as zero by a traffic volumemanagement of a MAC entity, and preventing battery power from beingconsumed. Generally, it takes about 10 seconds to release an RRCconnection in an actual WCDMA commercial network. Therefore, theoperating time of the timer may be determined by taking the time intoconsideration. Otherwise, the user may directly set the timer valuethrough a menu.

After the timer has been driven, the UE 200 proceeds to step 630, wherethe UE 200 determines if the UE 200 has received an RRC ConnectionRelease message from the RNC 300. The network, i.e. the RNC 300, maytransmit the RRC Connection Release message before the timer expires.When receiving the RRC Connection Release message, the UE 200 proceedsto step 660.

In contrast, when the UE 200 has not received the RRC Connection Releasemessage from the RNC 300, the UE 200 proceeds to step 640, where the UE200 determines if the timer “T_notraffic” expires. When the timer“T_notraffic” does not expire, the UE 200 returns to step 630.

In contrast, when the timer “T_notraffic” expires, the UE 200 transmitsan SCRI message to the RNC 300 in step 650, and transitions to the IDLEstate in step 660.

FIG. 6 is a flowchart illustrating a method for measuring the volume ofpacket data traffic by the UE according to an exemplary embodiment ofthe present invention. In step 680, the UE 200 measures packet datatraffic transmitted/received through an uplink channel and a downlinkchannel. That is, the UE 200 monitors the volume of packet data traffictransmitted/received between the UE 200 and the network. Next, the UE200 measures packet data traffic transmitted/received between the PDAunit 210 and the modem unit 230.

Although there is no packet data being transmitted or received betweenthe UE 200 and the network, there may exist packet datatransmitted/received between the PDA unit 210 and the modem unit 230.According to an exemplary embodiment of the present invention, whenthere is no packet data being transmitted or received not only betweenthe UE 200 and the network, but also between the PDA unit 210 and themodem unit 230, the SCRI message can be transmitted. Another exemplaryembodiment of the present invention may be implemented in such a mannerthat when there is no packet data being transmitted or received betweenthe UE 200 and the network, the UE 200 transmits the SCRI message, evenif there is packet data being transmitted/received between the PDA unit210 and the modem unit 230.

FIG. 7 is a flow diagram illustrating a mechanism for internallygenerating an SCRI transmission instruction by the UE according to anexemplary embodiment of the present invention.

When an event satisfying an SCRI transmission condition occurs, theinterface task section 216 notifies the RIL 214 that it is necessary toenter a PDP Preservation state in step 701. The PDP Preservation staterepresents a state in which a PDP connection is preserved while an Iusignaling connection has been released. When receiving the notificationthat it is necessary to enter the PDP Preservation state from theinterface task section 216, the RIL 214 transfers a notification for thePDP Preservation to the operating system 212 in step 703.

When receiving the notification for the PDP Preservation from the RIL214, the operating system 212 calls an RIL Application ProgrammingInterface (RIL API) in step 705. Then, in step 707, the RIL 214instructs the interface task section 216 to transmit an SCRI message tothe network according to the called RIL API. In step 709, the interfacetask section 216 instructs the RRC to transmit the SCRI to the RNC 300,in response to the instruction of the RIL 214.

Meanwhile, although the embodiment of the present invention has beendescribed about a case where the UE transitions from the CELL_FACH stateto the IDLE state, the present invention may be applied to a case wherethe UE transitions from the CELL_DCH state to the IDLE state. In otherwords, even when the current RRC state of the UE is the CELL_DCH state,the method of the present invention may be performed if there is nopacket data traffic being transmitted or received between the UE and thenetwork.

As described above, the method according to the present invention cansolve a problem of unnecessarily increasing current consumption of theUE, which is caused because the network does not attempt to release theRRC connection or attempts to release the RRC connection too late,although there is no more packet data traffic actually being transmittedin the CELL_FACH state.

In detail, the method according to the present invention can be appliedto all WinCE-based 3G UEs using WCDMA data service, and can efficientlyhandle a current consumption increase due to problems resulting from thenetwork. In addition, the method according to the present invention canbe internally implemented by applying an additional algorithm to the UE,without a change in the existing 3GPP messages, and may be applied evento the network of an actual provider through interoperability testing(IOT) in the RNC/SGSN.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A system for transitioning a radio resource control (RRC) state of a user equipment to an idle state, the system comprising: a radio network controller configured to: receive, from the user equipment, a Signaling Connection Release indication (SCRI) message configured to release a Signaling Connection while maintaining a Packet Data Protocol (PDP) connection, and transmit an RRC Connection Release message to the user equipment in response to receiving the SCRI message from the user equipment, wherein the user equipment is configured to: measure a volume of packet data traffic transmitted by or received by the user equipment, transmit the SCRI message upon determining that the packet data traffic has not been generated during a predetermined time, and transition the RRC state of the user equipment to the idle state in response to receiving the RRC Connection Release message from the radio network controller.
 2. The system as claimed in claim 1, further comprising a Serving General Packet Radio Service (GPRS) support node configured to connect to the radio network controller via an Iu interface, wherein the radio network controller is configured to transmit an Iu Release Request message to the GPRS support node upon receiving the SCRI message, and is configured to transmit the RRC Connection Release message upon receiving an Iu Release Complete message.
 3. The system as claimed in claim 1, wherein the user equipment is further configured to: monitor the volume of packet data traffic transmitted or received between the user equipment and a network.
 4. The system as claimed in claim 1, wherein: the user equipment is further configured to notify a radio interface layer (RIL) to enter a PDP preservation state when packet data traffic transmitted by or received by the user equipment has not been generated during the predetermined time; and the RIL is configured to: transmit the notification for PDP preservation to an operating system, and instruct an interface task section to transmit the SCRI message to the radio network controller.
 5. The system as claimed in claim 4, wherein: the operation system is configured to call an RIL application programming interface (RIL API), and the RIL is configured to instruct the interface task according to the RIL API.
 6. The system as claimed in claim 1, wherein the system is a wideband code-division multiple-access (WCDMA) mobile communication system.
 7. The system as claimed in claim 1, wherein the user equipment is configured to measure the volume of packet data traffic transmitted by or received by the user equipment when the RRC state of the user equipment is changed to one of a CELL_FACH state and a CELL_DCH state.
 8. A method for transitioning a radio resource control (RRC) state of a user equipment to an idle state by the user equipment, the method comprising: measuring a volume of packet data traffic transmitted by or received by the user equipment; determining whether the packet data traffic has not been generated during a predetermined time; transmitting a Signaling Connection Release Indication (SCRI) message to a radio network controller upon determining that the packet data traffic transmitted by or received by the user equipment has not been generated during a predetermined time; and transitioning the RRC state of the user equipment to the idle state in response to receiving an RRC Connection Release message from the radio network controller, wherein the SCRI message is configured to release a Signaling Connection, while maintaining a Packet Data Protocol (PDP) connection.
 9. The method as claimed in claim 8, wherein transmitting comprises: notifying a radio interface layer (RIL) that it is necessary to enter a PDP preservation state when the packet data traffic transmitted by or received by the user equipment has not been generated during the predetermined time; transmitting a notification for PDP preservation from the RIL to an operating system; calling an RIL application programming interface (RIL API) by the operating system; and instructing the RIL to transmit the SCRI message to the radio network controller.
 10. The method as claimed in claim 8 further comprising: measuring the volume of packet data traffic transmitted by or received by the user equipment when the RRC state of the user equipment is changed to one of a CELL_FACH state and a CELL_DCH state.
 11. The method as claimed in claim 8, wherein instructing the RIL to transmit the SCRI message comprises instructing the RIL to transmit the SCRI message according to the RIL APL.
 12. The method as claimed in claim 8, wherein measuring the volume of packet data traffic comprises monitoring the volume of packet data traffic transmitted or received between the user equipment and a network in a mobile communication system.
 13. The method as claimed in claim 12, wherein the mobile communication system is a wideband code-division multiple-access (WCDMA) mobile communication system.
 14. A user equipment for transitioning a radio resource control (RRC) state to an idle state, the user equipment comprising: a modem unit configured to measure a volume of packet data traffic transmitted by or received by the user equipment, and to determine whether the packet data traffic has not been generated during a predetermined time; and a Personal Digital Assistant (PDA) unit configured to: instruct the modem unit to transmit a Signaling Connection Release Indication (SCRI) message to a radio network controller upon determining that the packet data traffic has not been generated during a predetermined time, and transition the RRC state of the user equipment to the idle state in response to receiving an RRC Connection Release message by the modem unit from the radio network controller, wherein the SCRI message is configured to release a Signaling Connection while maintaining a Packet Data Protocol (PDP) connection.
 15. The user equipment as claimed in claim 14, wherein the modem unit comprises a protocol task section configured to: monitor the volume of packet data traffic transmitted or received between the user equipment and a network, and provide information about the volume of packet data traffic to the PDA unit.
 16. The user equipment as claimed in claim 15, wherein: the PDA unit comprises an interface task configured to: receive from the protocol task section information about the monitored volume of packet data traffic, and notify a radio interface layer (RIL) to enter a PDP preservation state when packet data traffic transmitted by or received by the user equipment has not been generated during the predetermined time; and the RIL is configured to: transmit the notification for PDP preservation to an operating system, and instruct the interface task section to transmit the SCRI message to the radio network controller.
 17. The user equipment as claimed in claim 16, wherein: the PDA unit further comprises an operation system configured to call an RIL application programming interface (RIL API), and the RIL is configured to instruct the interface task according to the RIL API.
 18. The user equipment as claimed in claim 14, wherein the modem unit is configured to measure the volume of packet data traffic transmitted by or received by the user equipment when the RRC state of the user equipment is changed to one of a CELL_FACH state and a CELL_DCH state.
 19. The user equipment as claimed in claim 14, wherein modem unit comprises a protocol task section configured to monitor the volume of packet data traffic transmitted or received between the user equipment and a network in a mobile communication system, wherein the mobile communication system is a wideband code-division multiple-access (WCDMA) mobile communication system.
 20. The user equipment as claimed in claim 14, wherein a length of the predetermined time is based on battery power consumption of the user equipment. 